Gas-treating apparatus

ABSTRACT

A gas-treating apparatus for causing a nonhomogeneous stream of gases to flow through a casing and to become homogeneously mixed in a relatively short span of time and space. A baffle extends laterally from the inner surface of the casing partially across the casing so that the outside streamlines of the forward flow do not attach readily to the inner surface of the casing. The inner edge of the baffle defines an opening which has an area and shape that correspond with the cross-sectional area and shape of the casing.

United States Patent Inventors John D. Nesbitt Toledo; Klaus H. l'lernsath, Sylvanla, both 01 Ohio Appl. No. 861,714 Filed Sept. 29, 1969 Patented Sept. 21, 1971 Assignee Midland-RossCorporation Toledo, Ohio GAS-TREATING APPARATUS 22 Claims, 8 Drawing Figs.

US. Cl 23/277 C, 110/8 A, 431/5, 431/202 Int. Cl F233 7/06 Field of Search 23/277 C; 48/180; 110/8 A, 18 A; 431/5, 202

References Cited UNITED STATES PATENTS 3/1959 Burden, Jr 23/277C 3,251,656 5/1966 Edwards 23/277 C 3,311,456 3/1967 Denny et al 23/277 C 3,408,167 10/1968 Burden, Jr. 23/277 C 3,472,498 10/1969 Price et al 23/277 C Primary Examiner-Joseph Scovronek Assistant ExaminerR. E. Serwin Attorneys-Harold L Mensing and Peter Vrahotes ABSTRACT: A gas-treating apparatus for causing a nonhomogeneous stream of gases to flow through a casing and to become homogeneously mixed in a relatively short span of time and space. A baffle extends laterally from the inner surface of the casing partially across the casing so that the outside streamlines of the forward flow do not attach readily to the inner surface of the casing The inner edge of the baffle defines an opening which has an area and shape that correspond with the cross-sectional area and shape of the casing.

PATENTEDSEP21|971 3,607,120

JOHN D. #558177 BY KZAUS h! HEMSATH .ZFJ g. 3. Arroxms? GAS-TREATING APPARATUS BACKGROUND OF INVENTION Up to the present time there has been an unfulfilled need for a simple gas-treating device which is capable of homogeneousl *nixing large volumes of gases in a relatively short span of time and space. Gas mixing and treating apparatuses capable of treating large volumes of gas are particularly useful in drying and other heat-processing operations. Another use is in fume incinerators in which a small quantity of gaseous'fuel is burned and mixed with a large quantity of exhaust fumes or waste gases containing a low concentration of combustible material and sufficient oxygen to complete combustion. The fumes are purified by being raised to a sufficiently high reaction temperature and held at or above this temperature until incineration is completed. The efficiency of these devices is primarily dependent upon the ease and thoroughness with which they are able to mix the gas streams and also on the rate of mixing.

Gas mixing devices are quite common in burners and combustion apparatuses, but they generally involve complex means for dispersing one gas throughout another by means of turbulence. The turbulence needed for the mixing is created normally be a radical change in the velocity of a high-velocity gas stream which results in a severe pressure drop. An example of a method which is commonly used and which does produce a severe pressure drop is to break up a bulk stream of gasses into a plurality of small discrete streams by means of a grid plate or the like. Also, prior art gas-treating devices do not perform satisfactorily when they are required to mix a large volume of gas comprising two gas streams of low velocity and pressure. The problem of mixing becomes more severe when the ratio between the volumes of the two gasses is above 8:1 and particularly when it is between about 20:1 and 500:1.

SUMMARY OF INVENTION Generally speaking, the gas-treating apparatus of this invention comprises a casing having means for introducing gases at one end, a treating chamber adjacent the other end, and a baffle means located intermediate the ends. Although the apparatus may be used to uniformly mix a single heterogeneous stream of gases, the embodiments shown in the drawing will be described primarily with respect to the mixing together of two streams of different gases. The gases may be mixed in other than equal proportions, such as in the ratios mentioned above, in which case the gas stream having the greatest volume flows through the casing or duct and the other gas is injected into the interior of the main gas stream so as to form an confluent gas stream curtain in the main stream. The lateral cross section of the gas curtain is lineal and is concentric with or roughly parallels the inner surfaces of a cylindrical or rectangular casing. Preferably the casing is cylindrical and the lateral section of the curtain is annular in form. In thermal gas treating apparatuses, such as fume incinerators, the injected gas which produces the gas stream curtain may be a fuel gas and the injecting means may be a ring or line burner and may have a flame stabilizer.

Downstream from the gas stream curtain injection means is a baffle which extends laterally across the casing from the inner surface of the casing. In has an opening which corresponds in shape to the lateral cross-sectional shape of the gas stream curtain and is axially aligned therewith.

OBJECTS AND ADVANTAGES It is a general object of this invention to produce a gas-treating apparatus which is capable of homogeneously mixing in a relatively short span of time and space a large bulk stream of gases flowing under low pressure.

It is another object of this invention to produce such an apparatus which will efficiently mix a heterogeneous gas stream without causing a severe pressure drop.

It is still another object of this invention to produce a gastreating apparatus which is capable of mixing in approximately two duct diameters not only gas streams flowing at very low velocities, just sufficient to cause turbulence, but also gas streams flowing at intermediate or high velocities.

It is still another object of this invention to produce a gastreating apparatus for efficiently raising a bulk stream of gases to a uniform temperature.

It is yet another object of this invention to produce a simple and efiicient fume incinerator which is economical to operate and maintain.

The above-mentioned objects and other objects and advantages and the manner of attaining them will be apparent from the following description of embodiments of this invention made with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view in perspective of a fume incinerator having a relatively small diameter and adapted for operating at low to moderate incineration temperatures. Portions of the apparatus have been broken away to show interior and underlying details.

FIG. 2 is an enlarged plan view taken along line 22 of FIG. 1 with parts broken away.

FIG. 3 is an end view of a fume incinerator similar to that shown in FIG. 2, but for operating at moderate to high incineration temperatures and having a polygonal ring burner adapted for use in a relatively large diameter casing.

FIG. 4 is a side view in section of the ring burner and mixing baffle portions of the fume incinerator in FIG. 3.

FIG. 5 is a side view of a ring burner similar to that shown in FIG. 4, but with a surrounding band-type flame stabilizer associated with the ring burner.

FIG. 6 is an elevation view in perspective of a fume incinerator with a rectangular duct having modular baffles.

FIGS. 7 and 8 show representative baffles for large cylindrical and rectangular ducts respectively, each having alphabetical symbols denoting areas and dimensions.

DETAILED DESCRIPTION OF THE DRAWINGS The gas treating or mixing apparatus will be described primarily with reference to a fume incinerator in which a stream of fuel is injected directly into the interior of a stream of fumes and ignited. The fume stream is homogeneously mixed with the burning or burned fuel stream by baffle means and thereby is thermally treated or incinerated in a subsequent chamber. Fumes as used herein shall include any gaseous fluid containing oxygen and also containing an oxidizable material in the form of a gas or finely divided droplets or even solid particles capable of being suspended in the gaseous fluid stream. Such fumes may be evolved from industrial processes, chemical reactions, and the incomplete oxidation or burning of combustible material. The ratio between the oxygen and the combustible material in the fume may be such that the fume is near or below the threshold of flammability at the temperature it is introduced into the treating apparatus.

Referring to the drawings, FIGS. 1 and 6 show fume incinerators l0 and 20 comprising vertically disposed heat treating or incinerating chambers 22 and 24 respectively. The incinerating chambers 22 and 24 need not be vertically disposed, but may be arranged horizontally or in other attitudes. 37 HORIZONTALLY OR IN OTHER A'I'IITUDES. These incinerators may be installed in or adjacent the exhaust stack or in some other portion of a fume exhaust system remote from the exhaust stack. The incinerating chamber 22 is defined by a cylindrical wall, such as the base portion of an exhaust stack, while the incinerating chamber 24 is defined by a rectangular wall, such as a section of duct. Both chambers are fabricated from materials which are capable of withstanding normal incinerating temperatures of between about l,200 F. to 1,500 F. A duct section sub assembly 26 or 28 containing the fuel injecting means and a baffle means is connected in fluid communication with the inlet end of each chamber 22 or 24 for conveying fumes into these chambers. A blower 30 or other means causes a stream of fume to flow through each duct and then through the respective chamber 22 or 24 at a velocity sufficient to cause turbulence. 'Ine Reynolds number indicating the fluid flow conditions in these chambers may be as low as 2,300.

Upstream from the inlet end of each incinerating chamber, a fuel injecting means is provided for supplying a curtain of fuel gas directly into the interior of the fume stream so that the 1 curtain of fuel gas is isolated from the walls of the incinerator by a surrounding portion of the fume stream.

The fuel-injecting means may be straight, circular, or polygonal in form and be made of apertured or slotted tubes or tubes having a plurality of jet nozzles provided that it is capable of producing a curtain of fuel gas within the fume stream.

FIG. 1 shows an annular fuel injecting means 32 for producing a hollow or tubular gas curtain stream in the interior of a fume stream flowing through the duct. The fuel-injecting means is concentrically mounted in the duct and has a plurality of jet nozzles 34 directed parallel with its axis and spaced equally around the annular manifold or distributor 36. The jet nozzles may be placed sufficiently close together so that if the fuel from one of them is ignited, the others will become ignited thereby. The fuel gas may be supplied at a relatively low pressure equivalent to about 1 inch of water column by means of a feed pipe 38 extending through the wall of the duct and connected to the distributor. The ratio of the volume of fuel to the volume of fume is approximately between 1:20 and 1:500, depending upon the amount and composition of the combustible material in the fume and on the temperature of the incoming fume. A flame retention or stabilizing means, such as an annular bar 39 having a T-shaped cross section, may be placed directly in front of the jets a short distance downstream therefrom so that an ignitable fuel-air gas stream is obtained adjacent the downstream side of the stabilizing means. It was found that a remarkably stable flame was obtained with the annular burner apparatus.

The incinerator subassembly 40 shown in FIGS. 3 and 4 is similar to subassembly 26 of FIG. ll, but is designed for moderate to high-temperature operation, for example in about a 1,400 F. to 1,700 F. range, for incinerating fumes which are difficult to incinerate, such as fumes containing soot or sootforming hydrocarbons. The inside of the duct portion of subassembly 40 preferably has protective layer 41 of insulative or refractory material.

The fuel injecting means 42 and burner apparatus in FIGS. 3 and 4 are similar to those of FIG. 1, but are in the form of a polygon, such as an octagon, in which eight fuel injecting segments 43 are each centrally fed and supported by a fuel line 44, extending radially from a common manifold 45 in its center. The flame retention bar 46 is also octagonal.

FIG. shows a wheellike fuel-injecting means 47 in which the fuel is directed slightly outwardly against and along an adjacent peripheral flame retention rim 48. The fuel orifices or jets may be axially angled to produce a slightly spiraling hollow columnar flame. In all of the annular and polygonal fuelinjecting means 32, 42, and 4,7 the fumes flow interiorly and exteriorly of the hollow gas curtains or flames produced thereby.

The fuel injection means in FIG. 6 comprises a pair of fuel distributing members 50 similar to straight line burners. The members 50 each supply fuel to their respective modular section of the incinerator. They are centrally disposed in their modular sections parallel with the sidewalls thereof and directly in front of an opening in a baffle which will be described later. A flame stabilizing bar 5 3 may be provided in confronting relationship to this fuel injecting means. 0n installations where the fume inlets are small or located off center with respect to the duct section 28, a diffuser or distributor such as a perforated plate 55 may be provided to distribute the fume stream evenly across the duct. In this embodiment, as well as in the others. the fuel gas or flame curtain is isolated from the walls ol'tho duct by a surrounding portion of fume.

In the incinerators shown, fume mixing baffles are provided on the downstream side of the fuel injecting means adjacent the incineration chamber inlet. Preferably the distance between the fuel injecting means and the fume mixing battle is less than about one-third of the diameter of mean dimension across the duct. Each bafile defines a central slot opening which corresponds with the lateral cross sectional shape of the associated fuel gas stream or flame curtain and is axially aligned therewith. The slot opening need not be entirely open. It may be obstructed partially, such as bya grid screen, struts 57, or the like, provided that the gas stream parted by the obstruction becomes confluent in a short distance downstream.

In FIGS. 1, 2, and 5 the mixing baffle 58 comprises a flat circular disc with an annular slot opening 60 formed by and between an annular rim member 62 and a concentrically mounted circular hub member 64. In small installations, such as where the inner diameter of the rim member is 12 inches or less, a hub member is not required and the rim member may block as much as 85 percent but not less than 50 percent of the opening. In the larger installations the rim member may block between 35 and percent of the opening and the hub member may block from 10 up to 50 percent of the opening. The effective open area of the slot opening is preferably between about 20 and 35 percent and suitably may be between 15 percent and 50 percent of the cross-sectional area of the incinerating chamber inlet. The remaining 50 to 85 percent of the opening is blocked by the bafile members 62 and 64. The relative length of the average or center diameter of the annular slot opening with respect to the diameter of the casing is such that Dsd,+u',, 1.6 where D is the inside diameter of the casing d, is the inside diameter of the annular slot defined by theperiphery of the hub member 6 1i, and d is the outside diameter of the slot defined by the inner circumference of rim member 62. Preferably 1.3 0s dH-d s 1.5 D (see FIG. 7). The proportions between the effective areas of the hub area A, the annular slot area B, and the rim member area C are such that A l-C/B is between about 1 and 5.7, preferably between 1.3 and 4, also AsC The range of the slot length/slot width (W,,) ratio defined as [1r(dri-u' l/ZW is greater than 2 and preferably between about 4 and 40. The hub member 64 may be displaced axially upstream or downstream from the plane of the rim member 62 is a slight distance, such as less than one-fourth of the duct diameter, for higher or lower velocity streams respectively. Also, the

baffle rnay be streamlined on its input side.

The baffle nieans 68 shown in FIGS. 3 and 4 is the same as V baffle means 58 except that the rim member 70 and hub member 72 of baffle 68 have been segmented by radially extending slots '74 and 76 respectively. Also the downstream side of the baffle means has been protected by a layer 78 of insulative and refractory material. Preferably the edges of the layer 78 which define the annular slot 79 are inclined so as to provide boundary layer separation.

The rectangular incineration chamber 24 of the incinerator 20 of FIG. 6 has a modular baffle system comprising two adjoining modules. More or fewer modules may be used, depending upon the size of the incinerator and the number of corresponding fuel injecting members to be used. The incineration chamber 24 may be divided axially by a partition 80 into two modular sections, each of which has a baffle member 82. The baffle members have peripheral rims which extend laterally across a portion of the sections from the inner surfaces of the surrounding walls and partition. The rims define generally rectangular central openings which are confrontingly aligned with the fuel injecting members 50 located upstream therefrom. A central baffle may be provided in a portion of the baffle opening, but is not'essentiul when the area and width of the opening are small, such as 0.5 of a square foot or less than 6 inches in width. The fuel gas and fumes are directed vertically downward towards the baffles 68. The relationships expressed above with respect to annulnrly slotted baffles apply to rectangular slotted baffles. Reference may be made to FIG. ti wherein a rectangular buffle, having a rim member and a central member, has been given primed reference characters corresponding with the reference characters on similar parts of the annularly slotted baffle of FIG. 7.

The peripheral and central recirculation regions formed respectively on the downstream side of the rim and hub members preferably extend axially downstream about equal distances from the plane of the rim member of each embodiment.

The effectiveness of the mixing may be shown by the temperature uniformity attained at approximately two duct diameters downstream from the baffle during a test run. In the test the entering fume was about 375 F. and the flame temperature was approximately 2,500 E, producing a temperature nonuniforrnity on the order of 2,100" F. temperature at 60 inches downstream from the baffle in a 36-inch diameter duct was between l,400 F. and 1,425 E, with an average of l,4l3.5 F. The nonuniformity of 25 F. is about 1 percent of the temperature nonuniformity on the upstream side of the baffle. This was achieved with a pressure drop on only 0.95 inch of water column.

While the principles of this invention are described above with reference to specific embodiments, it is to be clearly understood that this description is made only by way of example, and not as a limitation to the scope of this invention. For example, the teachings of this invention could be applied to a burner, makeup air heating, industrial burners, catalytic fumetreating devices, and the like.

We claim:

1. A gas-treating apparatus comprising: a casing, means for conducting a first gas stream through said casing, means located interiorly of said casing and said first gas stream for injecting at least one gas stream curtain having a lineal lateral cross section into the interior of said first gas stream, and a mixing baffle means downstream from said injecting means, said baffle means having a rim member extending laterally inward from the surface of said casing a substantially uniform distance thereby defining an opening in said baffle which is symmetric with the outer cross-sectional surface of said gas stream curtain, the downstream surface of said rim member substantially planar so as to provide a recirculation region therebeyond.

2. A gas-treating apparatus according to claim 1 wherein said rim member substantially blocks a peripheral area of a size of about 35 to 85 percent of the lateral cross-sectional area of said casing.

3. A gas-treating apparatus according to claim 2 wherein said baffle means further includes a central baffle member which effectively blocks between about to 50 percent of said cross-sectional area of said casing and said rim member effectively blocks between about 35 to 75 percent of said casing area forming an elongated slot opening between the rim member and central member of said baffle.

4. A gas-treating apparatus according to claim 3 wherein said slot opening is located in the inner 67 percent of the outer peripheral 75 percent of said casing area.

5. A gas-treating apparatus according to claim 3 wherein said casing is a cylindrical casing and said elongated slot opening is a substantially continuous annular slot formed between a rim member and a concentrically disposed hub member of said baffle.

6. A gas-treating apparatus according to claim 5 wherein the center diameter of said annular slot is between about 0.5 and 0.8 of the inside diameter of said cylindrical casing.

7. A gas-treating apparatus according to claim 6 wherein said center diameter is between 0.65 and 0.75 of said inside diameter of said casing.

8. A gas-treating apparatus according to claim 1 wherein said baffle means defines a lineal slot having an area of between about 15 to 50 percent of the lateral cross-sectional area of said casing.

9. A gas-treating apparatus according to claim 8 wherein the effective area of said slot is between about to 35 percent of the lateral cross-sectional area of said casing.

10. A gas-treating apparatus according to claim 1 having a means for injecting a plurality of said gas stream curtains, and said baffle has an equivalent number of said slot openings each of which is aligned with a corresponding gas stream curtain.

11. A gas-treating apparatus for homogeneously mixing in a short span of time and space two gas streams in volumetric proportions of above 8:1, said apparatus comprising: a casing, means for conducting a first gas stream through said casing, means for injecting at least one gas stream curtain into the interior of said first gas stream, said gas stream curtain having a lineal lateral cross section, and a mixing baffle means having at least one lineal slot opening which is symmetric with said cross section, said baffle means has a rim member and a hub member, said rim member has a substantially unifonn width which extends laterally inward from the inner surface of said casing and substantially blocks a peripheral area of a size about 35 to 75 percent of the cross-sectional of said casing, said hub member is centrally located with respect to said rim member and blocks an area of a size of about 10 to 50 percent of the cross-sectional area of said casing.

12. A gas-treating apparatus according to claim 11 wherein said casing is cylindrical and said elongated slot opening is a substantially continuous annular opening located in the inner 67 percent of the outer annular 75 percent of the cross-sectional area of said casing.

13. A fume incinerator comprising: a casing, means for conducting a stream of fumes through said casing, a burner located interiorly of said casing and said fume stream for producing at least one curtain of hot gases having lineal lateral cross section, said burner including a fuel injector and a flame stabilizer bar confronting said injector, mixing baffle means in said casing downstream from said burner, said bafile means having at least one opening which is symmetric with the outside surface of said curtain, and a fume combustion chamber downstream from said baffle means.

14. A fume incinerator according to claim 13 wherein said baffle has a rim member which extends inwardly from the inner surface of said casing and substantially blocks a peripheral area of a size of about 35 to 75 percent of the lateral cross-sectional area of said casing.

15. A fume incinerator according to claim 14 wherein said baffle means also has a plurality of narrow slots extending outwardly from its inner edge towards its outer edge.

16. A fume incinerator according to claim 13 wherein the downstream side of said baffle means is protected by an insulative refractory material. I

17. A fume incinerator according to claim 14 wherein the size of the slot area in said baffle means is between about 15 to 5 0 percent of the lateral cross-sectional area of said casing.

18. A fume incinerator according to claim 14 wherein said casing is a cylindrical casing and said elongated slot is a generally annularly shaped slot formed between a rim member and a concentrically disposed hub member.

19. A fume incinerator according to claim 18 wherein the size of said annular slot is between about 15 and 35 percent of the lateral cross-sectional area of said casing and said annular slot is located in the inner 67 percent of the outer peripheral 75 percent of said cross-sectional area.

20. A fume incinerator according to claim 14 wherein said burner is a ring-type burner for producing a hollow columnar curtain of gases.

21. A fume incinerator according to claim 20 wherein said ring-type burner has segments arranged to form substantially an equilateral polygon in a plane perpendicular to the mass flow of fumes, said segments each being centrally fed by a radially extending fuel line connected to a central fuel supply hub.

22. A fume incinerator according to claim 14 wherein said baffle is located downstream from said burner a distance equivalent to less than one-third the mean lateral cross-sectional dimension of said casing.

UNITED STATES PATENT OFFICE CERTIFICATTL Ol CORRECTION Patent No. ,120 Dated September 21, 1971 Inventor(s) John D. Nesbitt and Klaus H. Hemsath It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 25, after "normally" delete "be" and substitute therefor by line 50, after "form" delete "an" and substitute therefor a line 62, delete "In" and substitute therefore It Column 2, line 63, delete "37 HORIZONTALLY OR IN OTHER ATTITUDES. line 72, after "section", insert or Column 4, line 31, after "1.6" insert D line 35, delete "di" and substitute therefore d line 43, after "62" delete "is".

Column 5, line 15, before "temperature" insert The line 20,

after "drop" delete "on" and substitute therefore of line 41, before "substantially" insert being line 66, after "between insert about Column 6, line 1, after "of" delete "the lateral" and substitute therefore said line 18, after "cross-sectional" insert area Signed and sealed this 4th day of April 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. A gas-treating apparatus according to claim 1 wherein said rim member substantially blocks a peripheral area of a size of about 35 to 85 percent of the lateral cross-sectional area of said casing.
 3. A gas-treating apparatus according to claim 2 wherein said baffle means further includes a central baffle member which effectively blocks between about 15 to 50 percent of said cross-sectional area of said casing and said rim member effectively blocks between about 35 to 75 percent of said casing area forming an elongated slot opening between the rim member and central member of said baffle.
 4. A gas-treating apparatus according to claim 3 wherein said slot opening is located in the inner 67 percent of the outer peripheral 75 percent of said casing area.
 5. A gas-treating apparatus according to claim 3 wherein said casing is a cylindrical casing and said elongated slot opening is a substantially continuous annular slot formed between a rim member and a concentrically disposed hub member of said baffle.
 6. A gas-treating apparatus according to claim 5 wherein the center diameter of said annular slot is between about 0.5 and 0.8 of the inside diameter of said cylindrical casing.
 7. A gas-treating apparatus according to claim 6 wherein said center diameter is between 0.65 and 0.75 of said inside diameter of said casing.
 8. A gas-treating apparatus according to claim 1 wherein said baffle means defines a lineal slot having an area of between about 15 to 50 percent of the lateral cross-sectional area of said casing.
 9. A gas-treating apparatus according to claim 8 wherein the effective area of said slot is between about 20 to 35 percent of the lateral cross-sectional area of said casing.
 10. A gas-treating apparatus according to claim 1 having a means for injecting a plurality of said gas stream curtains, and said baffle has an equivalent number of said slot openings each of which is aligned with a corresponding gas stream curtain.
 11. A gas-treating apparatus for homogeneously mixing in a short span of time and space two gas streams in volumetric proportions of above 8:1, said apparatus comprising: a casing, means for conducting a first gas stream through said casing, means for injecting at least one gas stream curtain into the interior of said first gas stream, said gas stream curtain having a lineal lateral cross section, and a mixing baffle means having at least one lineal slot opening which is symmetric with said cross section, said baffle means has a rim member and a hub member, said rim member has a substantially uniform width which extends laterally inward from the inner surface of said casing and substantially blocks a peripheral area of a size about 35 to 75 percent of the cross-sectional of said casing, said hub member is centrally located with respect to said rim member and blocks an area of a size of about 10 to 50 percent of the cross-sectional area of said casing.
 12. A gas-treating apparatus according to claim 11 wherein said casing is cylindrical and said elongated slot opening is a substantially continuous annular opening located in the inner 67 percent of the outer annular 75 percent of the cross-sectional area of said casing.
 13. A fume incinerator comprising: a casing, means for conducting a stream of fumes through said casing, a burner located interiorly of said casing and said fume stream for producing at least one curtain of Hot gases having lineal lateral cross section, said burner including a fuel injector and a flame stabilizer bar confronting said injector, mixing baffle means in said casing downstream from said burner, said baffle means having at least one opening which is symmetric with the outside surface of said curtain, and a fume combustion chamber downstream from said baffle means.
 14. A fume incinerator according to claim 13 wherein said baffle has a rim member which extends inwardly from the inner surface of said casing and substantially blocks a peripheral area of a size of about 35 to 75 percent of the lateral cross-sectional area of said casing.
 15. A fume incinerator according to claim 14 wherein said baffle means also has a plurality of narrow slots extending outwardly from its inner edge towards its outer edge.
 16. A fume incinerator according to claim 13 wherein the downstream side of said baffle means is protected by an insulative refractory material.
 17. A fume incinerator according to claim 14 wherein the size of the slot area in said baffle means is between about 15 to 50 percent of the lateral cross-sectional area of said casing.
 18. A fume incinerator according to claim 14 wherein said casing is a cylindrical casing and said elongated slot is a generally annularly shaped slot formed between a rim member and a concentrically disposed hub member.
 19. A fume incinerator according to claim 18 wherein the size of said annular slot is between about 15 and 35 percent of the lateral cross-sectional area of said casing and said annular slot is located in the inner 67 percent of the outer peripheral 75 percent of said cross-sectional area.
 20. A fume incinerator according to claim 14 wherein said burner is a ring-type burner for producing a hollow columnar curtain of gases.
 21. A fume incinerator according to claim 20 wherein said ring-type burner has segments arranged to form substantially an equilateral polygon in a plane perpendicular to the mass flow of fumes, said segments each being centrally fed by a radially extending fuel line connected to a central fuel supply hub.
 22. A fume incinerator according to claim 14 wherein said baffle is located downstream from said burner a distance equivalent to less than one-third the mean lateral cross-sectional dimension of said casing. 